The present invention relates in general to devices for pluviometric measurement by experimental determination of the characteristics of rain, such as the distribution of the sizes, of the velocities of the raindrops falling at a given location and of the times of arrival of the said raindrops.
Pluviometric measuring devices are already known in which the measurements are used for applications such as the real-time modeling of meteorological conditions for air transport, or the forecasting of disturbances caused by rain to telecommunications, in particular to microfrequency waves.
These devices implement various physical principles, the main ones being:
the gathering of raindrops in a container,
radar detection,
the detection of ultrasound pulses corresponding to the impacts of raindrops on a membrane,
the optical detection of the passage of drops through a light beam.
Neither traditional pluviometers (gathering of drops), nor radar detection pluviometers make it possible to obtain individual measurements on the size and the instants of passage of the drops detected.
As far as the other techniques are concerned, although they make it possible to access individual information on each raindrop, they do not make it possible to measure the size of small drops (and in particular to measure diameters of drops of less than 0.5 mm).
This limitation is penalizing:
in respect of the general characterization of rainfall, since the drops with a diameter of less than 0.5 mm constitute a non-negligible proportion of most rainfall spectra,
and more particularly with respect to determining the impact of rain on telecommunications, the drops of small diameter having a considerable influence in this area.
An aim of the present invention is to make it possible to produce a device able to retrieve spectra of moving raindrops and the distributions of their times of arrival for drop diameters of less than 0.5 mm.
U.S. Pat. No. 4,529,309 and U.S. Pat. No. 4,318,180 already disclose devices for measuring the diameter of particles passing through a measuring space, comprising optical emission means, reception means comprising at least one photodetector receiving at least part of the light emanating from the emission means after this light has passed through the measuring space, as well as processing means which receive the signal at the output of the sensor, the reception means comprising at least two such photodetectors which receive portions of the light emanating from the emission means, these portions being superposed along the general direction of movement of the particles.
For its part, the invention proposes a pluviometric device characterized in that the device is a pluviometric device for measuring the diameter of raindrops, the processing means comprising means for determining the value to which the intensity of the current at the output of a photodetector decreases during the passage of a drop in front of the photodetector and for deducing therefrom the individual diameter of the drop, the processing means furthermore comprising means for correlating the intensities of current at the output of one and the other of the two photodetectors so as to distinguish the passage of small drops in front of the latter with respect to the noise of the current intensities at the output of the photodetectors.
As will be understood through the description of an exemplary embodiment of the invention, given in the subsequent text, such a device makes it possible to detect moving raindrops of small diameter (down to 0.1 mm or less).
It furthermore makes it possible to determine the velocity of these particles, as well as their direction of movement.
Preferred, but nonlimiting aspects of the device according to the invention are the following:
the emission means comprise a light-emitting diode, as well as optical means for straightening the light emitted by the said diode into a parallel beam;
the reception means comprise at least two slits which are superposed along the general direction of movement of the particles and which separate the light having passed through the measuring space into two portions which are sent respectively to one and the other of the two sensors;
the reception means comprise, downstream of the slits, optical means for concentrating the light received on the sensors;
it comprises means for heating optical means of the reception means;
it comprises means for protecting the sensors from the ambient luminous radiation surrounding the device;
the processing means comprise means for determining the velocity of the raindrops;
the processing means comprise means for determining the instants of arrival of the raindrops;
the processing means comprise means for determining the direction of movement of the raindrops.